October 4, 2011

Carl Sagan wrote that if the Earth were the size of a globe our atmosphere at that scale would be about as thin as a single sheet of paper. Yet the air we breathe is so fundamental to life that even the tiniest changes in the composition of our air could cause cascading climate change on a global scale. While carbon dioxide is present in only trace amounts, scientific consensus indicates at a change from 292 parts per million today to 380 parts per million by the next century could spell disaster for human civilization through rising sea levels, changes in established wind and ocean currents, melting ice caps and desertification associated with the overall average trend of global warming. And so atmospheric regulation is essential to the continuing survival of all life; this biogeochemical process is mainly controlled by single-celled organisms.

Our atmosphere on Earth is mostly made of nitrogen, but it’s also about 20% oxygen. Oxygen is a corrosive gas that is dangerous under high concentrations because of how reactive it is with other chemicals. But this concentration of oxygen has been by no means stable over the last four-and-a-half billion years; oxygen levels in our atmosphere have been virtually non-existent until about half a billion years ago, when the so-called Great Oxidiation Event (GOE) took place. The GOE released huge plume of oxygen into the sky over the course of a few million years, radically altering the compostition of life on Earth and giving rise to the ancestors of the eukaryotes. Early life on Earth was anaerobic, meaning that it could function without oxygen. While aerobic animal life takes in oxygen and burns it during metabolism to create carbon dioxide and energy as waste, anaerobic life uses a myriad of metabolic pathways to produce energy, reducing molten iron, acetate, sulfate, hydrogen gas, or other inorganic molecules to produce their energy.

It wasn’t until the rise of cyanobacteria that any appreciable oxygen could be produced. These cyanobacteria are blue-green algae that performed photosynthesis by taking in sunlight, carbon dioxide and water to grow. One byproduct of this reaction was oxygen gas. The early Earth environment was highly reducing, meaning that it would readily absorb any oxygen and quickly oxidize something in the environment. Substrate like iron (III) dissolved in the water would readily oxidize and become iron (II) oxide, which was insoluble in water and would sink to the bottom of primordial seas. We find these banded iron deposits around the world and they are a ready source of the iron we use in modern manufacturing. The presence of banded iron formations would indicate the presence of oxygen being produced by cyanobacteria at the time, so we can reasonable assume that aerobic photosynthesis was going on around 2.1 billion years ago. In fact, cyanobacteria were so pervasive on Earth that their combined exhalations of oxygen radically altered the composition of air.

Areios’s atmosphere is mostly nitrogen, like the Earth’s atmosphere, but the outgassing of volcanoes and the rapid destruction and creation of crust means that oxygen is less abundant in the atmosphere, which has profound implications for the development of animal life. Combine this with the later start for photosynthesis, and this means that aerobic life doesn’t appear until about 12 billion years into Areios’ existence, yet this kind of more complex life persists for over 3 billion years before the surface temperature gets too hot for photosynthesis to maintain itself permanently. Fifteen billion years after creation, the planet’s atmosphere undergoes another profound change. As Hemera gets brighter, the atmosphere would start to slump off and this would alleviate some of the heat that gets trapped in the Areiosan atmosphere. Eventually the atmosphere becomes so thin with carbon dioxide that there isn’t enough CO2 to fuel photosynthesis and plants would die off en-masse. This drop in carbon dioxide would eliminate the greenhouse effect on Areios, and in turn this massive die-off would incite the next ratcheting up of carbon dioxide, which would in turn lead to a positive temperature feedback loop. Oceans would boil over until the last life left on the planet would paradoxically resemble the earliest life; a halophilic thermophile. Eventually, even this hardy creature wouldn’t be able to survive Areios would once again be a world sterile of all life. Temperature would still rise, though, and would boil the carbon dioxide out of the carbonate rocks in the crust, causing a runaway greenhouse effect like the one that we see on Venus. Sadly, this is the fate of all terrestrial planets as their parent star grows old; the same fate awaits our own planet earth in the coming eons.

Long after the Earth's atmosphere boils away, our Sun will evolve into a Red giant star.

March 1, 2011

In the very center of Areios is the core, a dense ball of iron and nickel that sloshes around inside the planet, generating a magnetic field like the one on Earth. The core is divided into an inner and outer layer, based on density and these two layers spin at different rates, causing a magnetic field to form from an induced dipole moment. The magnetic field on Earth is generated by the molten iron and nickel that gets swirled around by the tug of the Earth’s orbit. The magnetic field was actually induced by the magnetic field generated from the Sun, and kept going by the motion of the liquid iron outer core which can conduct electricity as it was churned by the Coriolis Effect.Magnetic Pole reversal

Because Areios will take longer to cool, its core won’t differentiate into inner and outer layers until much later in time relative to how it happened on Earth. Because the core won’t differentiate at first, there won’t be a magnetic field on Areios until the planet’s insides settle down. This is important because that magnetic field keeps solar wind from stripping the atmosphere away and it keeps out deadly radiation that would attack the organic machinery of cells. In the book The Life and Death of Planet Earth, Peter Ward describes what some astrobiologists believe happened to Venus and Mars when the magnetic field of a planet stops; solar wind tears water into hydrogen and oxygen, boiling away the atmosphere until the atmospheric pressure prevents water from collecting on the surface at any temperature. The result: a dry and frozen world like Mars, or a dry and broiling world like Venus. Because Areios won’t develop a magnetic field until later on, life probably couldn’t start until the radiation bombarding the planet could be deflected. Thankfully, Areios regenerates its atmosphere through volcanic venting and it has enough gravity to hold on to some of the gases that would otherwise leak out of an Earth’s sized planet’s atmosphere, so the atmospheric stripping one would expect from Hemera’s solar wind can be kept at bay, or at least mitigated for a while.

This magnetic field reverses from time to time, and we have evidence of this on earth in iron-bearing minerals that have spewed out onto the crust from the mantle. In the Atlantic Ocean, there are areas where new crust is being created; magma from the mantle forces its way onto the surface as lava that cools and forms the ocean floor. As it solidifies, new material pushes the old material out of the way as more lava wells up from the mantle in a process called seafloor spreading. Magnetized iron in mineral crystals from the mantle record which way the magnetic field is spinning at the time when it hardens into rock. These rocks record a trend of increasing or diminishing magnetization of iron in the mantle and they show evidence that over geologic time, the poles will reverse with the North Pole flipping down to the South Pole and vice versa. During the process where the magnetization flips, there are periods of weak magnetization that can be disastrous for life because this causes more ionizing radiation to leak through the atmosphere.

On Areios, the thicker mantle keeps the insides of the planet too hot to differentiate the mantle and core into two distinct layers until later on in Areios’ history. That means that for the earliest period in Hemera’s stellar life cycle, Areios is unprotected by the cosmic rays that Hemera would bring onto Areios’ surface. Only after Hemera stops blasting the surface of Areios with radiation does Areios develop a magnetic field. Four billion years after the formation of Areios, we see a number of habitability factors line up for the first time; Hemera stops having such violent solar flares, the bulk structure of the planet settles down to trigger its magnetic field, the planet’s volcanism shoot out less gas, which causes a geologic ice age period. All of these converging factors lead to the first Areiosan lifeforms, the Areia.